Eaton easyE4 Manual page 640

10. Connection to other devices
10.2 Modbus TCP
10.2.2.3 Read Holding Registers 0x03:
636
Function 0x03 reads internal registers (e.g., marker words in the easyE4) word by
word.
Table 115: Request-PDU
Function Code 1 byte
Start address 2 byte
Number of 2 byte
registers
Response to the request being received
1. The starting address is analyzed (distributed among bytes 1 and 2)
a. Byte 1 = Hi; Byte 2 = Lo
2. The number of registers is analyzed (distributed among bytes 3 and 4)
a. Byte 3 = Hi; Byte 4 = Lo
3. The data words are read from the start of the (starting address) to (starting
address + number of registers)
A register corresponds, e.g., to one marker word
Table 116: Response-PDU
Function Code 1 byte
Bye Count 1 byte
Register values n* 2 byte Value
n= Number of registers read
Preparation for sending the response
1. The registers read (marker words) are mapped to two bytes per register
2. There are a high byte and a low byte for each register (marker word)
Example
Register word Hi0x02
l
Register word Lo0x2B
l
Content of marker word 0x022B
l
3. The LSB within the byte is bit 0
Once the response is encoded, it is sent.
easyE4 10/19 MN050009 EN www.eaton.com
0x03 ;Read Holding Registers
Must always be 1 less than the starting input you want
(zero-based)
1 to 125 (0x7D)
0x03 ;Read Holding Registers
A value of
= 2 * n must always be entered here